1. Field of Invention
The present invention relates to a spiral cold electrode fluorescent lamp, and more particularly to a spiral electrode fluorescent lamp whose second electrode is coated with a layer of gas absorbent for slowing the decaying rate of the same.
2. Description of Related Arts
A compact fluorescent lamp (CFL) is widely used for lightening. A conventional CFL includes a light tube, spread with a phosphor coating on its inner surface, containing inert gas and mercury substance, in the form of mercury vapor or liquid mercury. The light tube is enclosed with caps at its two ends, at which a first and second electrodes are disposed therein. When enough electric voltage is applied to the first and second electrodes, the second electrode emits electrons and causes the mercury to discharge, thereby conducting the electric current to the first electrode. In the course of discharge, the mercury emits ultra violet rays which excite the phosphor coating to generate visible light. The second electrode is usually shaped as a wire in a dimension of millimeter. In order to electrically excite the mercury to emit ultra violet rays, the second electrode is usually required to function at a temperature about 800 degrees Celsius.
A cold electrode fluorescent lamp (CCFL) has a basic structure similar to CFL in the sense that they all need a light tube with an inner layer of phosphor coating that contains inert gas and mercury substance, and a second electrode electrically connected to a power source for exciting the mercury. The CCFL is different from the CFL in the sense that the second electrode of CCFL has a larger surface area and lower functioning temperature. The second electrode of CCFL is usually shaped as a single or multiple layers of plates, such that its surface area is larger than the wire-shaped second electrode of CFL. Additionally, only a temperature about 100 degrees Celsius is required for the second electrode of CCFL to function. This is how the name “cold electrode” is given, comparing the traditional second electrode for CFL. Because the cold electrode functions at a lower temperature, the life span of CCFL usually lasts longer than its comparative models of CFL. Moreover, the CCFL can better survive an impact force than the CFL does, because it is easier for the impact force to disconnect the wire-shaped second electrode of CFL from the power source than to disconnect the plate-shaped second electrode from the same.
One phenomenon causes the cold electrode to decay is its oxidation problem. Besides inert gas and mercury, the light tube always contains air either residually left in the light tube, or subsequently entered from the sealing into the same. During the manufacturing process, gases such as O2, CO, CO2 and H2O, may be existed in the light-tube and such residual active gases would facilitate the oxidation of the cold electrode. The oxidation decreases the intensity of electrons emitted from the cold electrode, and therefore reducing the luminance of the CCFL. Until the oxidation develops to a certain point, the cold electrode can no longer emit electrons with enough intensity to excite the mercury. At this point, the CCFL can no longer serve its purpose of illumination.
One solution to cope with the oxidation problem is to place a gas absorber in the light tube to absorb the oxygenic gas. The less the oxygenic gas exists in the light tube, the slower the cold electrode oxidizes, the longer the cold electrode is able to emit electrons with sufficient intensity. The life span of the CCFL is therefore increased. For example, a conventional color display may adopt a second electrode partially coated with a layer of gas absorbent based on barium alloy; a filament light bulb may contain gas absorber having phosphor as its predominating constitutient; and some high-end products of CFL include gas absorber made of alloy containing zirconium and aluminum. These various types of gas absorber serve the same purpose of absorbing oxygenic gas in order to lengthen the life span of the lights.
One shortcoming of the conventional gas absorber is its insufficient capability of absorbing the oxygenic gas. The gas absorber performs usually at an activation temperature as high as 900 degrees Celsius. The high activation temperature works in both ways. Although it helps the absorber to absorb the oxygenic gas, it facilitates the oxidizing reaction of the second electrode. However, it also requires an additional expensive manufacturing equipments to activate the gas absorber at 900 degrees Celsius to form activated gas absorber in order to absorb oxygenic gas at normal temperature. As a result, the cost of manufacturing the CCFL is inevitably increased and processing of making the same is likewise complicated.
Thus, what is needed is a CCFL containing a gas absorber in its light tube that has an improved capability of absorbing oxygenic gas and lower requirement for working temperature in order to lengthen the life span of the second electrode of CCFL.